166 PRACTICAL ORGANIC CHEMISTRY which is loosely corked, and placed in ice. Whilst triis solution is cooling to o° the diazotoluene chloride is prepared by adding the powdered sodium nitrite gradually to the j>- toluidine hydrochloride and stirring. The temperature sliould not rise above 10°. When three-quarters of the nitrite has l>een added, test occasionally with potassium iodide-starch paper until a drop gives an immediate deep blue or dark brown colouration. Add this solution gradually in portions of about 20 c.c. at a. time to the cold solution of the cuprous chloride, and shake up well after each addition. A thick crystalline mass of orange coloured needles, consisting probably of the diazo-copper salt separates, and, on standing, decomposes slowly, forming a dark-coloured liquid. After standing a short time, the liquid is distilled in stoa.m. The distillate is shaken up with a little caustic soda to remove cresol, and the chlorptoluene, which sinks to the bottom, is separated. The liquid is further shaken out with a little chloro- form, which is then added to the chlorotoluene, and the \vliole dehydrated with calcium chloride. The liquid is decanted, the chloroform distilled off and the residue collected at 115 - 165°. Yield, about 45 grams. 2O. CH3CCH4N2C1 = CH3CGH4C1 + N J Properties. — Colourless liquid ; b. p. 162° ; m. p. 7*4 Reactions.— Chlorobenzoic Acid. — Boil 10 grams ^- toluene with 20 grams permanganate dissolved in 500 c.c. of writer in a brine or calcium chloride bath, with upright condenser, for a day. The bath should keep the contents of the flask too i ling' briskly whilst the permanganate is gradually added. Trie oily drops of chlorotoluene will gradually cease to drip from tlio con- denser and the permanganate will be nearly decolourised. The precipitated manganese dioxide is now dissolved a.s sul- phate by passing in sulphur dioxide gas until the last trace of brown precipitate has disappeared. The colourless criloro- benzoic acid comes down in the acid solution on cooling*, and is filtered, washed with water, and recrystallised from Sjpirit ; m. p. 236°. The yield is theoretical. CH3.C6H4C1 + 03 = COOH. C6H4C1 + H2O. See Appendix, p. 284.